Acute and/or severe disorders are a common cause of emergency treatment or hospitalization. One of the most common disorders of this type is acute or breakthrough pain. In cancer patients, pain is usually treated with non-steroid anti-inflammatory drugs (NSAIDs) and opiates alone or in combination. Opioid-requiring cancer pain patients are usually given slow-release opiates (slow-release morphine or ketobemidone or transdermal fentanyl). A characteristic feature of cancer pain are periods of inadequate analgesia (breakthrough pain). Most often they are due to increased physical activity of the patient. However, treatment of breakthrough pain by administration of increased time contingent doses of long-acting analgesics causes adverse side effects such an excess sedation, nausea, and constipation.
Other disorders and conditions which require a fast-acting treatment are, for example, pulmonary edema, gastroesophageal reflux, insomnia and nephrolitiasis.
Presently available oral, rectal, or sublingual formulations have relatively lengthy onset times or erratic absorption characteristics that are not well suited to control acute disorders.
Conditions of acute operative/postoperative or traumatic/posttraumatic pain as well as pain due to severe disease (e.g. myocardial infarction, nephrolithiasis, etc.) is usually treated with opioid analgesics which are administered parenterally (by intravenous or intramuscular administration) to obtain a rapid onset of analgesia. In such cases, rapid-onset oral alternatives are of considerable therapeutic interest. Also for the treatment of other acute disorders, it is of considerable interest to provide fast-acting therapeutic compositions which may be administered orally instead of parenterally or rectally.
However, many pharmaceutically active agents which would be advantageous to administer orally are not suitable to be swallowed. They may, for example, be inactivated by the gastro-intestinal liquids, have a slow action because of a low solubility in the aqueous medium, or be highly susceptible to metabolism by gastro-intestinal enzymes and have poor absorption properties, as exemplified for peptide hormones. It is therefore more preferable to arrange for the active component to be taken up through the mucous membranes of the oral cavity. Here, the most preferred way of administration is via the sublingual route. In this administration, a dosage unit of the pharmaceutical composition is placed under tongue, and the active component is absorbed through the surrounding mucous membranes. However, with this way of administration, the risk that the patient swallows the medication by swallowing saliva is well known.
For the treatment of acute pain may be used fentanyl, N-(1-phenethyl-4-piperidyl)-propioanilide, or one of its pharmaceutically acceptable salts. This compound is an opioid agonist and shares many of the pharmacodynamic effects of opiates such as morphine and meperidine. However, compared to these opiates, fentanyl exhibits little hypnotic activity, rarely induces histamine release, and respiratory depression is more short-lived. Fentanyl is commercially available for intravenous, intrabucchal (lozenge-transmucosal) and transdermal administration.
Following parenteral administration of fentanyl, the analgesic action is more prompt and less prolonged than that of morphine and meperidine. The onset of analgesia following i.v. administration is rapid. Peak analgesia is obtained within a few minutes. Following transbucchal administration by a lozenge, consumption of the lozenge is usually complete within 30 min and peak plasma concentrations appear after around 20 minutes, as described by e.g. Farrar et al., J. Natl. Cancer Inst., 1998, 90(8), p. 611-616. Analgesia is apparent within 5-15 min and peaks at about 20-50 min. While this is an improvement over oral administration for gastrointestinal uptake, a quicker onset of analgesia would be of substantial benefit to the patient. In addition, substantial amounts of lozenge-administered fentanyl are swallowed by the patient. This is not desirable and results in the administration of excessive amounts of the drug, which may give rise to side effects.